How to make skinned mesh with multiples parts (like r15 skinned mesh)?

[TenerPVPs]

1. What do you want to achieve?

   I saw the Skinned MeshParts are live! topic, and i want make a r15 skinned mesh avatar.

2. What is the issue?

   I dont understand how its possible, usually the skinned models i saw have just 1 Mesh part and a lot of bones

   

   I Dont understand how its possible make with multiples parts, like the example that we can download on the topic

   

3. What solutions have you tried so far?

   I looked on dev forum but i found nothing about that, on youtube i couldnt found nothing too.